1. Prepare the sauce. Mix cornstarch to thin paste with water, then stir in shoyu and sugar. Set aside.
2. Heat wok until hot. Add peppercorns and dry-fry over gentle heat for 1-2 mins. Remove and crush in mortar and pestle. Set aside.
3. Add half of oil to wok and heat over moderate heat until hot. Add beef and peppercorns, increase heat to high and stir-fty for 3-4 mins until beef is browned. Remove wok from heat and tip beef and juices into bowl. Set aside.
4. Return wok to moderate heat. Add remaining oil and heat until hot. Add pepper, chiles, ginger and garlic and stir-fry for 2-3 mins until softened, taking care not to let ingredients brown.
5. Return beef and its juices to wok and stir to mix with vegetables. Stir sauce to mix, then pour over been and vegetables. Increase heat tio high and toss until beef is hot and all ingredients ar combined. Serve immediatly.